The IRS issued Revenue Procedure 2019-46[1] to update Revenue Procedure 2010-51 related to rules for using the optional standard mileage rates for business, charitable, medical or moving expense deductions. The modifications are made to reflect changes made to IRC §§67 and 217 by the Tax Cuts and Jobs Act (TCJA).

Those changes removed the ability for taxpayers to deduct miscellaneous itemized deductions and moving expenses through 2025. The new procedure makes clear that use of these special rules does not somehow “work around” those law changes to restore a deduction.

The Revenue Procedure describes the modifications to the rules as follows:

(1) Section 4.02 is modified to provide that a taxpayer may not use the business standard mileage rate to claim a miscellaneous itemized deduction during the suspension period.
(2) Sections 4.03 is modified to provide that a taxpayer may not claim a miscellaneous itemized deduction during the suspension period for parking fees and tolls attributable to the taxpayer using the automobile for business purposes.
(3) Section 4.04 is modified to provide that, under § 1016(a)(2), a taxpayer must reduce the basis of an automobile used in business by the greater of the amount of depreciation the taxpayer claims for the automobile or the amount of depreciation allowable. If a taxpayer uses the business standard mileage rate to compute the expense of operating an automobile for any year, a per-mile amount (published by the IRS in an annual notice) is treated as the depreciation claimed by the taxpayer and the depreciation allowable for those years in which the taxpayer used the business standard mileage rate.
(4) Section 4.05(4) is added to provide that a taxpayer may not use the business standard mileage rate to claim a miscellaneous itemized deduction during the suspension period for unreimbursed travel expenses.
(5) Section 4.06 is added to provide that a taxpayer who pays or incurs unreimbursed employee travel expenses during the suspension period that are deductible by the taxpayer in computing adjusted gross income may use the business standard mileage rate to compute an adjustment to gross income.
(6) Section 5.02 is modified to provide that the deduction for moving expenses during the suspension period does not apply unless the taxpayer is a member of the Armed Forces on active duty moving pursuant to a military order and incident to a permanent change of station.
(7) Section 6.03(2) is modified to provide that in using the fixed and variable rate (FAVR) allowance, an employee may not claim a miscellaneous itemized deduction during the suspension period for parking fees and tolls attributable to the employee driving the standard automobile in performing services as an employee.
(8) Section 7.06 is added to provide that if during the suspension period, an employee’s substantiated expenses are less than the employee’s actual expenses, the employee may not claim an itemized deduction for the excess amount.
(9) Section 7.08 (formerly section 7.07) is modified to provide that an employee’s amount computed under section 4 for the business standard mileage rate is an itemized deduction subject to the 2-percent floor and is not deductible during the suspension period.
(10) Section 8.04 is added to clarify that amounts paid under a mileage allowance to an employee regardless of whether the employee incurs deductible business expenses are treated as paid under a nonaccountable plan.[2]

The procedure notes that while it is not officially effective retroactively, the IRC law changes do apply prior to the date this ruling was released:

This revenue procedure is effective for (1) deductible transportation expenses paid or incurred on or after November 14, 2019, and (2) mileage allowances or reimbursements (a) paid to an employee or to a charitable volunteer on or after November 14, 2019, and (b) for transportation expenses the employee or charitable volunteer pays or incurs on or after November 14, 2019. Notwithstanding the effective date in this section 9, amendments made by the TCJA to §§ 67 and 217 are effective for any taxable year beginning after December 31, 2017, and before January 1, 2026.[3]

[1] Revenue Procedure 2019-46, November 14, 2019, https://www.irs.gov/pub/irs-drop/rp-19-46.pdf, retrieved November 14, 2019

[2] Revenue Procedure 2019-46, pp. 6-8

[3] Revenue Procedure 2019-46, p. 32